利用彈性可移動細線來增強FC-72池沸騰與流動沸騰熱傳之新奇方法研究

Abstract

最近這二十年來，IC產業蓬勃發展，半導體製程技術不斷精進，電子元件藉由製程上的突破，其線寬從18.0μm縮小至1.0μm，造成元件上的導線數不斷大幅增加，使得單位面積上的發熱量急遽升高，如何將所產生的高熱量迅速地移走，使電子元件避免發生高溫過熱燒毀之重大課題，受到IC產業高度重視。近年來，電子冷卻散熱的形式從傳統的單相自然對流、強制對流，轉變為以相變化熱傳方式來進行散熱，主要的原因是藉由較高的潛熱傳遞來帶走大量的熱量。另外散熱鰭片尺寸大小也從傳統的大型鰭片縮成奈微米針狀鰭片，在這些散熱鰭片中，主要是利用固定式散熱鰭片，鮮少有探討可移動非固定式散熱鰭片來增強熱傳於池沸騰及流動沸騰熱傳中。此可移動式散熱鰭片預計將可大幅提升沸騰時之氣泡脫離頻率，進而增強沸騰熱傳。本計畫擬以詳細的實驗量測和觀測來探討被動式可移動鰭片對池沸騰及流動沸騰熱傳之影響。由於鰭片的移動是靠沸騰時強烈的液體及氣泡流動所帶動，而且鰭片必須非常薄小，在機械加工製作上將較困難。因此本研究將以常用的細線取代一般鰭片，提高實驗之可行性。 因此，在本三年期研究計畫中(民國99年8月至102年7月)，我們將建立兩套實驗系統(池沸騰和流動沸騰系統)，以FC-72為工作流體來詳細探討被動式可移動非固定散熱細線在飽和及次冷態池及流動沸騰情況之下是否可大幅增強沸騰熱傳。除此之外，也將改變散熱細線之材質及幾何參數來作詳細研究。同時我門也將探討移動細線對氣泡特徵(氣泡脫離尺寸、頻率及加熱面成核密度)之影響，以釐清加裝可移動散熱細線時之沸騰熱傳機制。

In recent two decades, the quick development of the IC (Integrated Circuits) and semiconductor manufacturing technology has resulted in the breakthrough in the fabrication of the electronic devices. The line width has reduced from 18.0μm to 1.0μm and the number of lines increases substantially, causing huge increase in the dissipating heat in the electronic devices. How to quickly move the dissipation heat from the electronic devices to avoid device overheating is an important task. Thus the methods employed in electronics cooling changes from that based on natural convection and forced convection to phase change recently because of latent heat involved in the heat transfer process. Besides, the fins also reduce to micro size. These fins normally fixed firmly on heating surfaces. No attention has been paid to investigating the effects of movable and flexible fins on the enhancement of pool and flow boiling heat transfer. The use of movable and flexible fins is expected to greatly increase the bubble departure frequency in the boiling process, which in turn will enhance boiling heat transfer. The present study intends to explore how passive movable and flexible fins affect pool boiling and flow boiling heat transfer through a detailed experimental measurement and visualization of the boiling process. Since the fin movement is induced passively by the vigorous liquid motion and bubble ebullition during the boiling process, the fins should be relatively small and thin, which is difficult in manufacturing to some extent. In this study we will use fine wires to replace the conventional fins to facilitate the experiment and promote the feasibility of the study. Thus, in this three-year research project (August 2010 to July 2013) two sets of experimental apparatuses (pool boiling system ＆ flow boiling system) will be established to investigate how the movable and flexible fins in the form of fine wires affect the boiling heat transfer with coolant FC-72. Both the saturated and subcooled pool and flow boiling heat transfer augmentation will be examined. Besides, the effects of the wire material and geometry parameters will be studied. Moreover, we will explore how the bubble characteristics in the boiling flow, including the bubble departure diameter and frequency and active nucleation site density on the heating surface, are affected by the movable and flexible wires to delineate the associated mechanisms for the boiling heat transfer enhancement by the movable fine wires.